The Sedalia weekly bazoo. [volume] (Sedalia, Mo.) 187?-1904, 1887-10-04
ABOUT Thermometers,
Why the Useful Little Instruments Can MOI
Always BE Trusted.

-
Why the Useful Little Instruments Can Not
Always BE Trusted.
During the hot spell there is no in
strument that is studied more carefully
than the thermometer. Every one
wants TO know how hot it is each dsy,
and all continually consult these little
glass tubes. These vary sometimes
several degrees at the same instant
Said dealer in thermometers to re-
porter:
Thermometers are very often curl
Gus instruments. Sometimes we find
one that is all right at certain points,
and at others it will be several degrees
out of the way. These variations are
caused by irregularities in the tube.
The tubes are very frequently imper-
feet. When the tube is too large, of
course, the registration is several de-
grees lower than it should be. Some
times the tube is too small and then
the mercury shoots up higher than it
ought to. The tubes have to be sea-
sOned. This takes several months.
When glass is new it changes, expands,
contracts and warps almost as badly as
green wood. Very often, after buying
cheap thermometer, the customer has
brought it back and said it registered
one hundred degrees in the shade,
when the temperature was only ninety.
The best thermometers are made in
London. These imported thermome-
tiers are, however, very expensive.
Some very good ones are made in this
country at New Lebanon, ~ Y, and at
Rochester
How are they made?' was asked.
1.-The tube is blown to the size
wanted, the top being left open. The
bulb is then heated to expel the air, and
while heated the open end is inserted
into some mercury. As the tube cools
the mercury runs into the vacuum.
The open end is then sealed and the
tube placed on scale. Then it
is placed in water of known
temperature and the point to
which the mercury rises is marked.
Several tests like this are made before
The instrument is offered Tor sale"
How are the thermometers proved
10 be accurate?'
There is place at Harvard College
ior testing them. They are carefully
examined at different temperatures,
md any variation is marked. A certi-
icate is given with every instruments
hat is examined"
(which scale do yoa think is the
,est?''
1.-The centigrade is the one / think
hOuld be generally adopted. For the
lse of brewers there is a thermometer
bout three feet long with a bulb about
wo feet in length. The scale of this is
hort and is only marked for few de-
,rees above freezing point. Another
i'd instrument is of English make, and
an be read in the dark. The tube is
lied with green composition and
Ontains phosphorus. Spirit thermome-
ers are used for very cold climates, as
nercury cOngeals at thirty degrees be-
DIV zero. These can not be used to
Measure extreme heat, as above q GER
ain temperature the liquid expands too
asst; it bOils at one hundred and sixty
egrees. For very high temperatures
ne pyrometer takes the place of the
thermometer. The heat is measured
y the expansion of metals, and will
ccurately register up to seven hun
red degrees. Febrile thermometers,
'r the use of physicians, are very care
lilly made, and a certificate is sold
18th them indicating their variations
accuracy.-N Y NAL and
;rpress.